. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. VELUM OF OSTREA CHILENSIS 105 of the larvae, as suggested by Buroker (1985) for Ostrea spp. and by Mackie (1979) for freshwater bivalves (Pisidi- idae), and as demonstrated in O. chilensis by Chaparro ct al. (1993). The present paper examines the velar ciliature of the larva of O. chilensis, an extreme case in which the larva is brooded for almost the entire developmental period, and compares the ciliature morphologically with that of the planktotrophic larvae of related species, particularly other ostreids. Materials and Me
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. VELUM OF OSTREA CHILENSIS 105 of the larvae, as suggested by Buroker (1985) for Ostrea spp. and by Mackie (1979) for freshwater bivalves (Pisidi- idae), and as demonstrated in O. chilensis by Chaparro ct al. (1993). The present paper examines the velar ciliature of the larva of O. chilensis, an extreme case in which the larva is brooded for almost the entire developmental period, and compares the ciliature morphologically with that of the planktotrophic larvae of related species, particularly other ostreids. Materials and Methods Samples of oysters (Ostrea chilensis) were obtained at intervals throughout the brooding period (October to Janu- ary) during 1992, 1993. and 1994 from a natural bank in the Quempillen estuary in the northern part of Chiloe Island (41°52'S: 73°46'W). in the south of Chile. On each sam- pling date, several female oysters were opened and their embryos or larvae removed. In this way. all larval develop- ment stages were sampled. Larvae were prepared for scan- ning electron microscopy (SEM) following Hadfield and laea (1989). Larvae were anesthetized for about 10 min in a MgCl-, solution isotonic with seawater, then fixed for 1 h in ice-cold 3% glutaraldehyde in M sodium cacodylate buffer. pH Fixed samples were rinsed in the buffer solution twice and post-fixed for 1 h in ice-cold 1% OsO4 in M sodium cacodylate. pH The specimens were then rinsed two or three times with buffer solution and then once with distilled water before being dehydrated in a graded series of ethanol (Cragg, 1985). For SEM, dehydrated specimens were critical-point dried from liquid carbon dioxide in a Polaron E3000 drying apparatus. Dried larvae were attached to aluminum viewing stubs with double-sided tape and then coated with gold in an Edwards S150A sputter-coaler. When necessary, larval shells were broken with a fine needle to expose the internal structures (Cragg, 1985, 1989). Co
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